Use generic PrivateKey type rather than RSAPrivateKey

app/src/main/java/com/limelight/nvstream/http/LimelightCryptoProvider.java

@@ -1,11 +1,11 @@
 package com.limelight.nvstream.http;
 
+import java.security.PrivateKey;
 import java.security.cert.X509Certificate;
-import java.security.interfaces.RSAPrivateKey;
 
 public interface LimelightCryptoProvider {
     X509Certificate getClientCertificate();
-    RSAPrivateKey getClientPrivateKey();
+    PrivateKey getClientPrivateKey();
     byte[] getPemEncodedClientCertificate();
     String encodeBase64String(byte[] data);
 }